COPT Enters Into $1 Billion Line Of Credit & $400 Million Term Loan

COLUMBIA, MD August 9, 2011 — Corporate Office Properties Trust (COPT) (NYSE: OFC), a specialty office real estate investment trust (REIT) that focuses primarily on serving the specialized requirements of U.S. Government and Defense Information Technology tenants, announced today that, on August 5, 2011, it entered into a credit agreement, to be effective September 1, 2011, that provides for a new, $1 billion line of credit (the “Credit Facility”) that matures on September 1, 2014, and may be extended by one year. The Credit Facility will replace the Company’s existing $800 million line of credit, which was due to mature September 30, 2011.

Also on August 5, 2011, the Company entered into a $400 million term loan agreement, also to be effective September 1, 2011 (the “Term Loan”), that has a four-year initial term and a one-year extension option. The Company is using proceeds from the Term Loan to replace its existing $225 million Revolving Construction Facility, which was due to mature in May 2012. COPT intends to use the remaining proceeds from the Term Loan for general corporate purposes, including any repurchases of the Company’s 3.50% Exchangeable Senior Notes due 2026 that the Company may be required to make during the upcoming repurchase period relating to the notes upon the exercise by noteholders of their repurchase option.

On the Credit Facility and Term Loan, J.P. Morgan Securities LLC and KeyBanc Capital Markets acted as joint lead arrangers and joint book runners; KeyBank National Association acted as administrative agent; JPMorgan Chase Bank, N.A. and Bank of America, N.A. acted as co-syndication agents; Barclays Bank PLC, PNC Bank, NA, Royal Bank of Canada and Wells Fargo Bank, NA, served as co-documentation agents; and Manufacturers and Traders Trust Company, Regions Bank and SunTrust Bank served as managing agents.

“We were pleased to strengthen and expand our banking relationships during the negotiations of the new, $1 billion line of credit and $400 million term loan, which enable us to extend our debt maturities at attractive interest rates,” stated Randall M. Griffin, Chief Executive Officer of COPT.

Company Information

Corporate Office Properties Trust (COPT) (NYSE: OFC) is a specialty office real estate investment trust (REIT) that focuses primarily on strategic customer relationships and specialized tenant requirements in the U.S. Government and Defense Information Technology sectors and Data Centers serving such sectors. The Company acquires, develops, manages and leases office and data center properties that are typically concentrated in large office parks primarily located adjacent to government demand drivers and/or in strong markets that we believe possess growth opportunities. As of June 30, 2011, the Company owned 269 office properties totaling 21.4 million rentable square feet, which includes 20 properties totaling 1.1 million square feet held through joint ventures. The Company’s portfolio primarily consists of technically sophisticated buildings in visually appealing settings that are environmentally sensitive, sustainable and meet unique customer requirements. COPT is an S&P MidCap 400 company and more information can be found at www.copt.com.

Forward-Looking Information

This press release may contain “forward-looking” statements, as defined in Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934, that are based on the Company’s current expectations, estimates and projections about future events and financial trends affecting the Company. Forward-looking statements can be identified by the use of words such as “may,” “will,” “should,” “could,” “believe,” “anticipate,” “expect,” “estimate,” “plan” or other comparable terminology. Forward-looking statements are inherently subject to risks and uncertainties, many of which the Company cannot predict with accuracy and some of which the Company might not even anticipate. Accordingly, the Company can give no assurance that these expectations, estimates and projections will be achieved. Future events and actual results may differ materially from those discussed in the forward-looking statements.

Important factors that may affect these expectations, estimates, and projections include, but are not limited to:

• general economic and business conditions, which will, among other things, affect office property demand and rents, tenant creditworthiness, interest rates and financing availability;

• adverse changes in the real estate markets including, among other things, increased competition with other companies;

• the Company’s ability to borrow on favorable terms;

• risks of real estate acquisition and development activities, including, among other things, risks that development projects may not be completed on schedule, that tenants may not take occupancy or pay rent or that development or operating costs may be greater than anticipated;

• risks of investing through joint venture structures, including risks that the Company’s joint venture partners may not fulfill their financial obligations as investors or may take actions that are inconsistent with the Company’s objectives;

• changes in our plans or views of market economic conditions or failure to obtain development rights, either of which could result in recognition of impairment losses;

• governmental actions and initiatives, including risks associated with the impact of a government shutdown such as a reduction in rental revenues or non-renewal of leases;

• the dilutive effect of issuing additional common shares; and

• environmental requirements.

The Company undertakes no obligation to update or supplement any forward-looking statements. For further information, please refer to the Company’s filings with the Securities and Exchange Commission, particularly the section entitled “Risk Factors” in Item 1A of the Company’s Annual Report on Form 10-K for the year ended December 31, 2010.